- Trisomy 21- More than 90 % of Down syndrome cases are caused by trisomy 21. An extra chromosome (chromosome 21) originates in the development of either the sperm or the egg. When the egg and the sperm unite to form the fertilized egg, three (rather than two) chromosomes 21 are present. As the cells divide the extra chromosome is repeated in every cell.
- About half of babies with Down syndrome have heart defects
- Some defects are minor and may be treated with medications, while others may require surgery
- visual problems include crossed eyes, near- or farsightedness, and cataracts.
- may have hearing loss because of fluid in the middle ear, a nerve defect, or both
- increased risk for thyroid problems and leukemia
Normally in reproduction, the egg cell of the mother and the sperm cell of the father start out with the usual number of 46 chromosomes. The egg and sperm cells both undergo a cell division in which the 46 chromosomes are divided in half, so that both the egg and the sperm cells will have 23 chromosomes each. When a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, the baby will have a complete set of 46 chromosomes, half from the father and half from the mother.
Some parents have a rearrangement called a balanced translocation, in which the #21 chromosome is attached to another chromosome, but it does not affect their own health
Is it mutational?
- Its not a mutation, its extra genetic material on the 21st chromosome called trisomy 21, mutation is a changing of the chromosomes or alleles. How is it inherited ?
- It is an extra copy of chromosome 21, which is not the sex chromosome. It is also neither dominant nor recessive because it is not caused by a certain allele, or form, of one gene; it is an entire extra chromosome. Instead of 2 chromosome 21's there are three and therefore there is an extra copy of every gene on the chromosome. Therefore a person wouldn't be AA or aa for any of the genes, but rather AAA, AAa, Aaa, or aaa. And that would just be for one gene.
- it is neither ressesive or dominate
- There is no specific treatment for Down syndrome. A child born with a gastrointestinal blockage may need major surgery immediately after birth.
How is it diagnosed?
- A doctor can often make an initial diagnosis of Down syndrome at birth based on how the baby looks. The doctor may hear a heart murmur when listening to the baby's chest with a stethoscope.
- A blood test can be done to check for the extra chromosome and confirm the diagnosis.
- There are more than 400,000 people living with Down syndrome in the United States.
- Down syndrome occurs in people of all races and economic levels.
- i learned that when a baby is born with down syndrome there hand designs is straight.
- honestly they aren't any different than we are